1. Field of the Invention
The present invention relates to a test structure for a semiconductor process and a method for monitoring said semiconductor process, and more particularly, to a test structure and a monitoring method for detecting the charged particles on the surface of a semiconductor substrate.
2. Description of the Prior Art
Manufacturing a semiconductor involves many sub-semiconductor processes such as the process for depositing the material layer, the process for defining patterns on the material layer, etc. In the chemical vapor deposition (CVD) process, the semiconductor substrate is exposed to a precursor or a plurality of precursors, and a chemical reaction occurs on the surface of the semiconductor substrate enabling the depositing of the material layer. The material layer includes an insulating layer made of silicon oxide or high-K (high dielectric constant) materials, or a conductive layer made of polysilicon, metal or alloy. A plasma enhanced chemical vapor deposition (PECVD) process takes advantage of plasma to accelerate the chemical reaction rate, which is applicable under low temperature conditions; consequently, the PECVD process is commonly implemented in the semiconductor process. Moreover, with the miniaturization of integrated circuits (IC), in addition to a lithography process, an anisotropic etching process is also significant for defining the patterns, for example, reactive-ion-etching (RIE) plasmas are used extensively in the etching process to achieve a high degree of pattern definition and precise dimensional control.
During the plasma process, such as the PECVD process detailed above, the surface of the semiconductor substrate is bombarded by plasma ions, and charged particles such as electrons collect on the surface of the semiconductor substrate or in the exposed semiconductor devices. After several plasma processes, the accumulated charged particles may cause the performance of the semiconductor device to deteriorate, and even break the semiconductor device. Accordingly, monitoring wafers individual to the production wafers are used to detect the stability of the semiconductor process. For example, a CHARM-2 wafer is used to monitor the damage caused by the charged particles, and the electrically erasable programmable read only memory (E2PROM) can be taken as a test structure in the CHARM-2 wafer. The complicated structure of the E2PROM increases the manufacturing cost of the CHARM-2 wafer, however. Additionally, the monitoring wafer may recognize the divergence of the semiconductor processes, but will fail to reflect the status of the production wafers. Consequently, how to simplify a test structure for detecting charged particles in order to decrease the cost of a monitoring wafer and achieve monitoring the production wafers is still an important issue in the field.